Method of erasing a nonvolatile memory for preventing over-soft-program

A method of erasing a nonvolatile memory for preventing over-soft-program, the method comprising:

• performing an erase operation on at least one cell among a plurality of cells in the nonvolatile memory;
• applying a first soft program verify operation to determine whether a threshold voltage of the cell is lower than a first verify voltage;
• applying a second soft program verify operation to determine whether the threshold voltage of the cell is lower than a second verify voltage, wherein the second verify voltage is lower than the first verify voltage;
• determining whether the threshold voltage of the cell is lower than the first verify voltage and determining whether the threshold voltage of the cell is lower than the second verify voltage;
• performing a soft program operation with a first soft program voltage when the threshold voltage of the cell is lower than the first verify voltage and higher than the second verify voltage;
• and
• performing the soft program operation with a second soft program voltage higher than the first soft program voltage when the threshold voltage of the cell is lower than both of the first verify voltage and the second verify voltage.